netdev - Re: [PATCH net-next 1/4] tsnep: Throttle interrupts

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Message-ID: <Y3aatP+384keCkpN@lunn.ch>
Date:   Thu, 17 Nov 2022 21:33:56 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        edumazet@...gle.com, pabeni@...hat.com
Subject: Re: [PATCH net-next 1/4] tsnep: Throttle interrupts

On Thu, Nov 17, 2022 at 09:14:37PM +0100, Gerhard Engleder wrote:
> Without interrupt throttling, iperf server mode generates a CPU load of
> 100% (A53 1.2GHz). Also the throughput suffers with less than 900Mbit/s
> on a 1Gbit/s link. The reason is a high interrupt load with interrupts
> every ~20us.

Not my area of expertise, but is NAPI working correctly? It should be
that you disable interrupts while NAPI is polling, and only re-enable
interrupts when polling has stopped. If you are receiving at near line
rate at 100% load, i would of thought that NAPI would be polling most
of the time and interrupts would be mostly disabled?

Interrupt coalescence makes a lot of sense thought, so the patch
itself is useful.

       Andrew